The present invention relates to a check valve, in particular for use in rock drill bits of the type that comprise a drill body, the upper part of which body having a bore and adapted to be connected to a drill tube, and the lower part of which body comprises a number of projecting legs, the lower ends of the legs carrying rotatable cutters provided with cutting inserts.
When drilling in rock with roller drill bits, compressed air is used for conveying crushed rock (cuttings) from the bottom of the drill hole to the top thereof. In order to bind the cuttings and lessen the formation of dust, the flushing air is often mixed with water. The flushing air is also used for cooling and cleaning the bearings of the rotating rollers that carry the cutting inserts. These bearings are unfavorably affected by water in the flushing air.
Furthermore, problems arise when drilling in rock ground containing water, where cuttings and water are liable to penetrate through the flushing jet orifices in the drill head to a valve that is used for preventing further upward penetration. This happens when the flushing air is shut off, usually when extending the drill tube. The valve is usually made in such a way that water is separated from the flushing air which is conducted to the bearings. In this way the life of the bearings can be extended. It is thus known to use valves in drill bits of the type mentioned in the introduction, but sufficient attention has not been paid to the problems with water separation and protection of vital parts against intrusion of cuttings.
One object of this invention is to provide a check valve having an improved ability to separate water and to substantially reduce the risk for intrusion of cuttings and their effect on the function of the valve.
It is another object of the invention to provide a spring-biased valve which is less susceptible to fatigue stresses.